A greenhouse is a plastic or glass structure that can provide a suitable micro-climate for various crops and plants, protecting them from severe and variable outdoor weather conditions. During the daytime with intense solar radiation, the greenhouse effect caused by the absorption of solar radiation makes the temperature inside the greenhouse even higher than the ambient temperature; thus, plants and crops may suffer being dried due to high rate of evapotranspiration caused by the excessive heat, and their production may decline. To provide a suitable growing environment, cooling technologies are essential and must be introduced.It plays a vital role in the greenhouse industry especially in hot weather although it is still important in any other climate
conditions. The climate of Shanghai is humid subtropical and features hot, humid summers and chilly, damp winters. Table 1 shows the typical variation in climate conditions in Shanghai. Summer sees high temperature that plants and crops cannot endure; as a result, air cooling technology is urgently required. Over the past decades, many relevant studies and experiments of greenhouse cooling technologies have been conducted throughout the world. The method of computational fluid dynamics (CFD)and TRNSYS are applied to study the energy necessary. Therefore, shadings, which are very common in greenhouse construction, other than additional mechanical equipments are used to improve the cooling effect in humid regions. Such system taking full use of the existing components in the greenhouse is easy to control and cheap.
The purpose of this study was to evaluate the performance of evaporative cooling pad-fan system in greenhouses in a humid subtropical climate, extending the application from only in the dry climate to the regions with relatively high humidity. Experiments
were made with the objective of evaluating the combined effects of the fan–pad system and other methods. A 2304-m2 glass multi-span greenhouse installed with an evaporative cooling pad was studied. The temperature, relative humidity and air velocity were measured at different locations in the greenhouse. The effects of evaporative cooling combined with other methods such as external shading nets, internal thermal screens and circulation fans were investigated. Based on the experimental results, the idea of
using existing greenhouse components as assistants to improve the cooling effect of evaporative cooling fan–pad in subtropical area is feasible and it allows for less consumption in both energy and investment aspects compared with other options.